A geofence may be generated around a target location. The geofence may be used to detect a user that crosses into the target location surrounded by the geofence. The proliferation of smart phones, such as Apple's iPhone, has enabled wide spread usage of location based services and advertising due to the technical capabilities of such devices. Many smart phones come equipped with a GPS receiver capable of pinpointing a location of the smart phone. As such, many smart phone devices, when communicating with a server, also transmit the location of the smart phone when using location-based services.